This invention deals generally with so-called case knives, that is knives specifically designed to cut open corrugated cardboard packing cases or cartons. A problem with prior case knives is that it is very difficult to control the depth to which the blade, (usually a replaceable and disposable steel blade such as a single-edge razor blade), penetrates through the corrugated cardboard panel or edge of a case. Inadequate penetration can result in inefficiencies. For example, the lid or panel of the corrugated cardboard case will not fully separate from the base. Perhaps more importantly a case knife blade, if it penetrates too deeply into the corrugated cardboard panel, can damage the packing case contents. If the contents are foodstuffs, such too deep penetrations can result in spoilage or consumer rejection of the products, as for example when the case knife blade has opened the individual packages of food, such as breakfast cereals and the like. Another problem with prior case knives is the risk that the operator can be cut with the exposed edge or pointed end of the case knife blade. While some prior knives include spring-operated guards and the like, such guards tend to be cumbersome and even when operating properly, can still present an unduly high risk of injury to the operator.
U.S. Pat. No. 5,241,750 shows a case knife with a fixed blade 13 and a movable hood 12, which can be locked in a position that resists displacement away from the blade by arc 60. This hood consists of a generally U-shaped member. There are other such fixed blade case knives, such as U.S. Pat. Nos. 2,730,800, 4,744,146 and 6,233,832. In each disclosed device, the guard can be placed in a position to shield the knife blade. Other prior case knives include mechanisms for automatically withdrawing the blade into the handle of the case knife to prevent injury. Examples of these are U.S. Pat. Nos. 4,139,939, 4,713,885 and 3,641,667. One characteristic of these movable blade knives is a fairly complex blade positioning mechanism, which can result in higher manufacturing costs, poor operability, and difficulty in properly positioning the blade when the blade needs to be replaced.
Another problem with prior case knives is that they favor a right or left-handed operator. One prior case knife construction shown in U.S. Pat. No. 5,012,581 attempts to solve this problem by providing a case knife handle construction that accommodates a triangular blade in one of the two positions, so that the blade protrudes in a preferred position for either a right or a left handed operator. This system, however, requires the user to elect whether the case knife will be configured for use in the right or left hand when installing the blade. Once the blade is installed, the case knife cannot necessarily be easily operated with the opposite hand until the blade is re positioned in the handle.
Some prior case knives include a guard used to position the case knife at a proper distance along a right-angled edge or corner of a corrugated cardboard box. The purpose and intention of this guard is to assure that the blade of the knife penetrates the box at the ideal position along the edge of the box, while holding the blade to just sever a lid or panel of the box without penetrating the contents. One such prior case knife is shown in U.S. Pat. No. 2,376,887. Here, means 59 provides a guide for the blade along the edge or surface of a corrugated box.